Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already carry readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds real context beyond them: credential-free public AniList data (no auth needed) and the fact that per_page is clamped to 50, which changes how an agent should paginate. No error or rate-limit behavior is given, so not a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core action and returned fields, then auth model, then pagination, then the sibling pointer – a sensible order with no filler. Minor redundancy in repeating the parameter descriptions already present in the schema keeps it from a 5.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values need not be explained, yet the description still previews the cast fields. Combined with auth disclosure, pagination clamping, and the sibling alternative, an agent has everything required to call this correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, and the description merely restates the schema text for page and per_page ('1-based page number, default 1' / 'default 10, clamped to 50') rather than adding syntax or constraints the schema lacks. With the schema doing the heavy lifting, baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Returns an anime's cast') and enumerates the returned fields (character name, native name, billed role, image, favourites). The closing pointer to anime_character_search cleanly separates it from the sibling search tool, so an agent can route without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly names the alternative (anime_character_search) and the condition that selects it, which is the key routing decision given the near-identical siblings anime_character, anime_title_staff and manga_title_characters. It does not state any exclusions (e.g. when NOT to prefer this over anime_character detail lookups), so it stops short of a full 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.